Point contact semiconductor unit



N0v 29, 1955 R. A. LANGEVIN ETAL POINT CONTACT SEMICONDUCTOR UNIT Filed Jan. 25, 1954 IN VEN TORS.

ROBERT A. LANGEVIN EDMUND A. GSCHWIND FIG. 5

United States Patent O POINT CONTACT SEMICONDUCTOR UNIT Robert A. Langevin, Wellesley, and Edmund A. Gschwind, Framingham, Mass.,.assiguors to Clevite Corporation, Cleveland, Ohio, a corporation of Ohio Application January 25, 1954, Serial No. 405,922'

12 Claims. (Cl. 317-235) This invention relates to a point contact semiconductor unit.

The basic configuration of the point contact transistor includes a semiconductor, a base electrode having an ohmic contact with one face of the semiconductor, and a pair of small wire or cat whisker emitter and collector electrodes having spaced rectifying point contacts with the opposite face of the semiconductor. To achieve the desired electrical characteristics with these transistors it is necessary to establish a precise predetermined spacing between the emitter and collector electrode contacts on the semiconductor, this spacing ordinarily being of the order of .G02 inch to .008 inch. It is the common practice at present to establish this critical spacing between the emitter and collector electrode contacts through hand adjustment by human operators employing microscopes. This exacting hand operation is introduced at one' of the most critical points in the fabrication of point contact transistors and hence must be performed with great care and skill, adding substantially to the cost of the finished articles.

Since proper operation of point contact transistors depends upon maintaining the emitter and collector electrodes in contact with the semiconductor, it is necessary to exert a force on these electrodes to insure that they stay in contact with the semiconductor when the latter undergoes small displacements due to thermal expansion and contraction or other causes. Various expedients have been adopted for this purpose, including the incorporation in the electrodes themselves of some sort of formed spring structure which acts to maintain contact pressure of the electrode against the semiconductor throughoutsuch displacements. The formation of such spring structures presents formidable diiculties in view of the small electrode wire diameters, which may be as small as .003 inch, and the dissimilar materials of which the electrodes proper and the formed spring may be composed.

In addition, such point contact transistors in many cases require an impregnant for protecting the unit against moisture. At the same time this impregnant should allow the springs incorporated in the point contact electrodes to act, and in some instances the impregnant may mechanically damp these electrodes to some extent. The impregnant contacts the surface of the semiconductor and may be a source of contamination leading to defective operation and poor aging characteristics in the finished transistor. 2

vIt is the purpose of the present invention to provide a point contact semiconductor unit having novel provi sion for properly spacing the point contact electrodes, for

stressing the electrodes to maintain the electrodes in contact with the semiconductor at all times, and for moisture proofing the unit, all Without the ditiiculties and disadvantages associated with the prior art devices of this type. It is, therefore, an object of this invention to provide a novel and improved point contact semiconductor unit. vA further object of the present invention is to provide a novel point contact semiconductor unit having a novel arrangement for establishing and maintaining the proper spacing between the electrode point contacts on the semiconductor.

yIt is also an object of this invention to provide a novel point contact semiconductor unit having provision for stressing a point contact electrode in a novel and simpliiied manner to maintain it in proper contact with the semiconductor.

Another object of this invention is to provide a novel moisture resistant point contact semiconductor unit.

Still another object of this invention is to provide a novelarrangement which simplifies and economizes the fabrication of point contact semiconductor units.

In the preferred embodiments of the present invention, which is illustrated in the accompanying drawing and set forth in detail in the following description, the foregoing objects are accomplished by the provision of a semiconductor unit in which the semiconductor is received snugly within a housing, thev housing being formed with passages leading to the semiconductor which receive the electrode wires and-which are separated by a projection, the electrode'wires being stressed to bearV against this projection, ,so that theirspacing at their respective point contacts on the semiconductor is determined by the thickness of the projection, and also stressed to be maintained in Contact with theisemiconductor at all times'.

In the drawing:

Figure 1 is an exploded perspective view of a point contact transistor unit in accordance with the present invention, with the point contact electrodes omitted for clarity;

Figure 2 is a perspective view showing the front hous. ing section of the transistor unit;

Figure 3 isa front view of the unit, showing in dotted lines the manner in which the point contact electrodes are received in the housing and stressed to' maintain contact with the semiconductor;

Figure 4 is a transverse section on a reduced scale centrally through the unit along the line 4-4 in Fig. 3; and

Figure 5 is a section along the line 5 5 in Fig. 3.

Referring to the drawing, in accordance with the preferred embodiment of the presentinvention there is provided a two-piece housing consistingv of a rear section 10 anda smaller front section 11 adapted to be assembled in confronting relation with their'respective inner, generally flat faces 12 and 13 abutting against one another. Each of these housing sections is -molded of dielectric material which is substantially impervious to moisture. The rear housing section 10 is formed with a pair of integral dowels or studs 14 and 15' projecting forward from its inner face and adapted to be received snugly in complementary holes 16 and l17 extending through the front housing section 11. This arrangement facilitates the quick assembly together of the housing sections in the proper manner. I l

The housing sections 10 and-11 are formed with generally rectangular recesses or cavities 18 and' 19 respectively which are open at the confronting inner faces of the housing sections and which are aligned in general registration with one another, so that they define a single chamber or compartment for receiving the semiconductor when the housing sections are assembled together. A base insert 21, preferably of Monel metal, is molded integral with the rear housing section 10. This base insert adjacent its forward end rests on the bottom wall of the recess 18 in the rear housing section 1i). At its forward extremity the base insert 21 projects beyond the inner face 12 of the rear housing section lil and is disposed in spaced relation above the bottom wall ofthe recess 19 in the front housing section 11, as best seen in Fig, 4. Behind the recess 1 8 the base insert. 21..extcnds .cqmpleteb/thxcushand beraad .the rear housing section for connection to an appropriate electrical terminal. In back of the housing recess 18 the base insert 21 .is Vformed with a pair of holes 20a and .2017. (Fig. 5.) .into which the material of the rear housing section ow's when it is molded to anchor the base insert in place.

,A wafer 25 of semiconductor `material, such as germanium, is soldered to the upper .faceof base electrode 22, ,after which the base electrode. 22 is spot welded at 4its lower face to the upper 'face of the base insert 21. Thus, the base insert 21 serves as a lead-in conductor for the base electrode. ,The back `edge 23 of base electrode 22 abuts against the back wall 24 o'f the recess 18 in the rearf'housing section 10, as best seen in Fig. 4.. Thus, the base electrode locates the semiconductor wafer 25 at the desired position within the housing. Obviously, the base. electrode v22 contacts the semiconductor 25 completely across the lattersbottom face, providing a large area, low resistance, ohmic contact thereat on the semiconductor.

For receiving 'the point Contact v'electrodes the front housing section 11 is formed .at its `inner`face with a pair of spacedpassages 26 'and..27'having the`conguration shown in Figs. 2 and 3. These passages have relatively widely spaced openings each of which is relatively wide frorn front to back and from Vside vto side at the top of lthe front housing section. Shortly beloul their upper ends thesepassages becomefrelatively 'narrow from side to side, each with parallel side walls vspaced apart from .012 to 0.18 inch down to the recess 1i) inthe front housing section 11. Also, as bests'een in Fig. 4, the passages 26 and 27 each tapertoward the inner face 13 of the front housingsection 11in a direction down from the upper ends of these passages and become narrow from front to back, with an even 'depth of from .O08 to .012 inch `downto the recess 19 in one practical embodiment. Passages 26 a'nd`27 are separated by a spacer in the form "of `a wedge-'shaped nose 28 which is relatively wide at"its`.'p'pe`r end and 'which tapers down to a thin segment`28`a at Vitsjlower lend immediately above the recess '19. This v'thin segment 28a at the lower end lofr'iose'2`8 has'paralleljside faces spaced apart a distance suhstantiall'y equal tothe desired spacing between the l' electrode point'contacts Von Athe semiconductor, which 'in (lorie pra'ctical embodiment may befrom-.0045 to .0055 inch. fThe'outersides of the passages `26 and r27' adjacent tlie fup'per ends "of :these passages are formed `with curved {sholders"-29^nd '30, respectively, which'cnverge toward each 'other -in a direction down tow'ard'reces's'19.

The lead-'in 'conductors for the respective*point'oontact 'electrodes are 'in vthe form 4of-"piris 33 tand 34' of Monel metal which are ,molded linto' the `"rear housing section 1t). These pins'terrninatef'at Vtheir 'forward ends just beyond the front face `12 of the Vrear'housing section andexterid rearwardly therefrom ``tl'irou'ghy and beyond the rear housing section. '"As fshown in Fig. v4, each pin is formed with a knurled enlargedportiondisposed within'the rear housing sectionflt) torancho'ring the pin in the molded body 10.

ln the assembly of this unit, after the semiconductor 25 'and its base electrode 22 have been vproperly Yspot welded .to baseinsert 21 as shown in Fig. l, with the base insert 21 adjacent its forward 4end `resting on: the bottom of recess18`in'the-r`ear housing s'ec'tion,"the rear edge 23 of hase electrode 22 abutting' against I'the/back wall 24 of recess' 18, andthe semiconductor'25soldered to the upper face of baseel'ectrode 22,`t he Yfronthousing section 11 is then positioned'in'confronting 'relation with the rear housing`section,'with the respective inner faces of the housing sections-abutting against each other and the dowels 14 and'v 1S on :the rearhousing section received s'nu'glyin thefopenings 16p-and 17 in'vthe'front housing'se'ction. When fthspositi'oned, the hsingfsec- 4 tions are then welded together by means of a hot welding tool vcenr/enti'onal to the plastic industry.

Then, a pair of point contact electrodes in the form of thin, flexible, resilient wires or cat whiskers 31 and 32 of tungsten, phosphor bronze, orother suitable material, and having a diameter of the order of .005 inch, are inserted from the top or'z'e'nings down into the passages 26 and 27 until their sharpened, bevel-edged lower ends engage the upper face of the germanium wafer 25. The point contact electrode wires thus have rectitying, high resistance contacts 'on the semiconductor. These wires are then spread apart at 'their -upper 'ends until they overlie the 'forward ends of t-h'e flead in conductors 33 and 34. This causes the point contact electrode wires to bear against the curved 'shoulders 29 and 30 adjacent the upper ends of the passages 26 and 27, as shown in Fig. 3. This, in turn, stresses the wires so that adjacent their lower ends they -bear tightly against the parallel opposite sides of the thin nose segment 28a at the inner face of the front 'housing member 11. Since their sharpened edges -are in mutually adjacent relationship, the point contacts of `the electrode wires on the semiconductor are -spaced apart -by -the thickness of the lower segment 2da of the nose 28. With -th'e point Contact electrode wires stressed in this manner theyare then spot welded to the vfront -ends `of the -lead-in con-v ductors 33 and 34. vProm Fig. 3 it will be apparent that the connections of thepoint contact electrode wires 26 and 27 to the lead-in vconductors 33 and -34 maintain the electrode wires 4'spread'apart attheir upper ends and deformed, as described. This deformation of the normally straight point contact velectrode wires vstresses them so that at their lower ends-they conform tightly against the lower segment -28aof`thenose 28 and thereby have a spacing at their point Vcontacts on lthe .germanium wafer'determinedby the thickness of the thin nose vfsegment 28a. Thes'tressing of the point contact'velectro'de wires in this manner also imparts to ieach -of them .a downward component of force 'which maintains -'each in intimate contact with thevgermanium waferithroughout anydimensional changes iin'the-datterdue to v.thermal expansion or the like. Before insertion in'to'fthe housing the .electrodewires 31 and132 "may -be leither` straight or else `preformed to afparticularfshape, vnot straight, so that they arestressed in the desired manner, by 'being mounted as described, to exert' suitable 'forces against the'housing nose 23 and against the-semiconductor 25. This preforming of the electrode wires may' 'either add to'or subtract from the /stresseslinpo'sed fon the electrode wires "by 'being :assembled-in the housing vas described.

If desired, 'the upper-ends of the'electrode wires 26,-27

may bebent over 'to vlie flatacross the '-to'p oftlie rearfhous-- ing section`10, as indicatedfin Fi-gsx31and'4.

The transitor unit 3 may 'then "-be finished by "insertihgfit into a mold cavity somewhat larger than the unit-litself and vfilling the mold cavity with a `'suitable'-moistureresistant plastic, which 'coats the ottside fof th'e'lh'o'sing about 1/6 inch :thickand icompletely'sealsthe `unit against moisture. While the 'plasticsealsthe outer endsof fthe passages'26, 127, 'as Wellfas'anyf'other' openings' in the housing assembly, it -does'lnotlilow fdo'wnirito'the fhousing chamber to contaminate the'fsemiconductor 25 becau'sethe narrow passages 26,' 27 do -notpermit"`the escape of air` in these passages andYinthehousihgfchamber 18, 19flfor the semiconductor. In one practical embodiment, fthe passages 26; 27far1e feachO1Z'inh to .0-l8'rinch a'cross and .008 inch :to .OlZTinGhdeep. fiSin'ee-'the 4:electrode"wires themselves are '.(HXi'inCLIiA 'or' larger indarn'eter, the opening through each" passage 126,' 27 f down finto fthe housing chamber 18, -19 fori-the Tse'mic'onductor {is'linsiiient to permit the'escape of theltrappe'd air soA thatf the waterproofing plastic might'flow :dini/1n'l intothe chamber-to'fcontct the semiconductor. Therefore, thisiprovis'ion 'i for ywaiterproong the "semiconductor tinitldoes'not' result Einidontamination of: the'rs'eni'cordit'or.

From the' foregoing it will be apparent that'the` objects and purposes of the present invention are accomplished in an advantageous manner by the specific arrangement described above. However, it should be evident that the principles of the present invention may be incorporated into assemblies differing from the specific embodiment described above and illustrated in the accompanying drawing, as, 'for example, in point contact semiconductor devices diifering from the standard transistor included in the above-described unit. Therefore, while in the foregoing description andthe accompanying drawing there has been disclosed a specific preferred embodiment of the present invention, it is to be understood that various modications, omissions and refinements which depart from the specific disclosed embodiment may be adopted without departing from the spirit and scope of this invention.

We claim:

1. A point contact semiconductor unit comprising a semiconductor, a pair of exible, resilient electrode wires each having point contact with the semiconductor, a housing deiining a chamber receiving the semiconductor and formed with spaced passages extending into the chamber and receiving the point contact electrode wires, said passages being separated by a spacer, said electrode wires beyond said passages being spread apart greater than the spacing between the passages immediately adjacent said chamber, and said electrode wires beyond said passages being secured to lead-in conductors and thereby stressed to bear against said spacer immediately adjacent the chamber to have a spacing at the semiconductor determined by the spacer. l

2. In a point contact semiconductor unit, the combination of a semiconductor, a two-piece housing including a first housing section formed with a recess open at its inner face and a second housing section having its inner face abutting against the inner face of the second housing section, said second housing section being formed with a recess open at its inner face and communicating with said recess in the rst housing section and defining therewith a chamber receiving the semiconductor, one of said housing sections at its inner face being formed with a pair of channels communicating with said chamber and separated by a spacer integral with said housing section, said spacer immediately adjacent said chamber having closely spaced side walls at the channels which extend parallel to each other, said spacer in a direction away from said chamber becoming progressively thicker with its side walls at the channels diverging away from each other, a pair of exible, resilient electrode wires extending through said channels and having point contacts on the semiconductor in said chamber, and means stressing said electrode wires to force them against the spacer at said parallel side walls immediately adjacent said chamber so that the electrodes at their point contacts on the semiconductor are spaced apart a distance corresponding to the thickness of the spacer between said parallel side walls and stressing said electrode wires to press them against the semiconductor.

3. In a point contact semiconductor unit, the combination of a semiconductor, a two-piece housing including a pair of housing sections having abutting inner faces and formed with communicating recesses thereat which define a chamber receiving the semiconductor, one of said housing sections at its inner face being formed with a pair of channels communicating with said chamber and separated by a spacer integral with said housing section, said spacer immediately adjacent said chamber having closely spaced, parallel side walls at the respective channels, said channels being formed with outer side walls disposed opposite the respective side walls of the spacer and in a direction away from said chamber diverging away from each other, a pair of exible, resilient electrode wires extending through said channels and having point contacts on the semiconductor, said electrode wires beyond said channels in a direction away from said chamber being spread apart a distance greater than the spacing between the channels at their outer ends and secured fixedly thereat to stress said electrode wires against said outer side walls of the channels and thereby deform said electrode wires to bear against said parallel side walls of the spacer immediately adjacent said chamber to have a spacing at their respective point contacts on the semiconductor equal to the spacing between said parallel side walls of the spacer and to stress said electrode wires to vbear against the semiconductor.

4. The combination of claim 3, wherein said electrode wires are each normally straight.

5. The combination of claim 3, wherein said electrode wires are each preformed to modify the forces exerted on the electrode wires by their respective mountings on the housing.

6. In a point contact semiconductor unit, the combination of a housing having a chamber, a semiconductor in said chamber, said housing having a pair of adjacent passages leading into said chamber, and a pair of exible resilient electrode wires narrower than said passages and extending through said passages into said chamber and engaging the semiconductor in point contact fashion, said electrode wires being mounted on said housing to be stressed to bear against the semiconductor at their respective point contacts therewith and to bear against the adjacent walls of the passages adjacent said chamber to have a spacing at their point contacts on the semiconductor determined by the spacing between said adjacent walls of the pasages adjacent said chamber.

7. In a point contact semiconductor unit, the combination of a housing having'a chamber, a semiconductor in said chamber, said housing having a passage leading into said chamber, a ilexible resilient electrode wire narrower than said passage and extending through said passage into said chamber and engaging the semiconductor in point contact fashion, and means beyond said passage stressing said electrode wire to bear against a side wall of said passage immediately adjacent the chamber so that the position of the contact point of the electrode wire on the semiconductor is determined by the position of said passage side wall.

8. In a point contact semiconductor unit, the combination of a housing having a chamber, a semiconductor in said chamber, said housing having a passage leading into said chamber, and a exible resilient electrode wire extending through said passage into said chamber and engaging the semiconductor in point contact fashion, said electrode wire being mounted on the housing outside said passage to be deformed in said passage to exert contact pressure on the semiconductor.

9. In a point contact semiconductor unit, the com` bination of a housing containing a chamber, a semiconductor in said chamber, said housing having a passage leading from outside the housing into said chamber, and a exible resilient electrode wire narrower than said passage and extending through said passage into said chamber and having point contact with the semiconductor, said electrode being secured iixedly beyond said passage and stressed to bear against one wall of the passage adjacent the end of the passage remote from said chamber and bearing against the opposite side wall of the passage immediately adjacent the chamber so that the position of the electrode wire at its point contact on the semiconductor is determined by said opposite passage side wall.

10. In a point contact transistor unit, the combination of a pair of housing members abutting at their inner faces and formed with communicating recesses thereat defining a chamber, a base insert molded into one of said housing "17 e1eetrode,"and l'a pair fof electrodes lhaving point contact withtheffoppositefaeelf the semiconductor.

11. -Apontfcont-act transistor vunit 'comprising va twopiece housingincluding a -pairef'housing sections having abutting inner faces and formed with communicating recesses thereat -Whiclrdene a Chamber `for receiving a semiconductor, a base insert molded .into one of said housing-sections y'and extending therethrough into-said chamber, a base electrode secured to said base insert and :received-'in said Vchamber with one of `its side edges abutting against one wall of said chamber to position saidbase electrode 'properly within said chamber, a semiconductor-disposed in said chamber and secured at one of its faces i to Ithe ibase electrode, one --of 4said housing sections at its inner face being formed with a pair of channels communicating -With said "chamber and separated by a spacer integr-al yWith lsaid housing section, said spacer mmed-iatelyeadjacent said chamber having closely spaced, parallel si'defwallsat the respective channels, said'channels being'formed With outerside walls opposite the respective side Walls-fof the spacer which diverge'away from each other in a direction'away from said chamber, a .pair of flexible, resi1ient,'lelectrode wires Vextending through said channels vand Yhaving point vcontactsron the semiconductor, said electrodefwiresbeyond sa-idchannels'iin a direction away-from said chamber being spread Aapart-a distance greater -thanfthe spacing-between the channels at their outer'endsland secured -xedly thereat to stress-said electrode wires against said outer side lwalls of the channels and thereby to -fdeform lsaid electrode Wires to bear againstf-said/parallel'side Wallsrof the spacer immediately t8 adjacentsaid chamber :to lhave -a spacing :at their respective :point :contacts on the semiconductor fequal :to the spacing 'between said ="parallel side uwa'llstof 'Athegspacer v,and to stress -said electrode lwires fto fbear against .the semiconductor.

12. A point contact/transistorunit comprising a 'housing of vmoisture -resistant material, -said housing lhaving an A internal chamber, abase L insertf molded ,into saidfhousing and-extending yfrom :outside ythe 'housing `.into said chamber therein, a fbase Ielectrode secured f-to lsaid base within said housing ychamber, a semiconductor secured atene-of its l'faees :.tofsaidlbaseelectrode, ysaid housing being =1formed with a pair kof spaced lnarrow passages `leading :from :outside `the Ihousing into :said chamber at the opposite face fof the semiconductor, Va pair of electrode Wires-extending fromout'side the fhousing through said passages into said housing chamber and each having pointf contact Awith fsa-idopposite :face 4of .the semiconductor at spaced l locationsthereom anda coating of moisture resistantplastic ymolded around;the housing and renderingthe unit substantially moisture i'proof.

Vljerenccs Citedin the :le of .this patent UNITEDv STATES PATENTS 2,586,609 -Burke Feb. 19, 1952 2,634,323 .Pantchechnikoff Apr. 7, i1953 v2,673,311 Amico Man y23, 1954 2,686,279 -Barton Aug. 10, 1954 2,688,110 ,Dornaleski etal Aug.21, 1954 2,697,805 Collins Dec. .21, 1954 

1. A POINT CONTACT SEMICONDUCTOR UNIT COMPRISING A SEMICONDUCTOR, A PAIR OF FLEXIBLE, RESILIENT ELECTRODE WIRES EACH HAVING POINT CONTACT WITH THE SEMICONDUCTOR, A HOUSING DEFINING A CHAMBER RECEIVING THE SEMICONDUCTOR AND FORMED WITH SPACED PASSAGES EXTENDING INTO THE CHAMBER AND RECEIVING THE POINT CONTACT ELECTRODE WIRES, SAID PASSAGES BEING SEPARATED BY A SPACER, SAID ELECTRODE WIRES BEYOND SAID PASSAGES BEING SPREAD APART GREATER THAN THE SPACING BETWEEN THE PASSAGES IMMEDIATELY ADJACENT SAID CHAMBER, AND SAID ELECTRODE WIRES BEYOND SAID PASSAGES BEING SECURED TO LEAD-IN CONDUCTORS AND THEREBY STRESSED TO BEAR AGAINST SAID SPACER IMMEDIATELY ADJACENT THE CHAMBER TO HAVE A SPACING AT THE SEMICONDUCTOR DETERMINED BY THE SPACER. 